1. Field of the Invention
This invention relates to an electronic musical instrument in which a key depression signal transferred in the form of a coded digital signal is applied to one or more tone source circuits and waveshape information of the sound range corresponding to the key depression signal is read out and processed to obtain a musical waveshape of the frequency corresponding to a selected key.
2. Description of the Prior Art
In recent years, there has been proposed for electronic musical instruments a tone source device of the type in which one cycle of a required musical waveshape is prestored in a waveshape memory and the waveshape stored therein is read out by a tone source clock signal having a repetitive cycle proportional to a scale frequency to obtain a musical waveshape of each scale frequency.
With this method, however, a faithful reproduction of a complicated musical waveshape, especially a sound of an actual musical instrument, will require a waveshape memory of a very large memory capacity. Further, in the case of constructing the abovesaid tone source device by a conventional one key-one generator method, the device itself will become inevitably bulky and complicated. Then, the assignee of the present application has proposed novel methods in Japanese Patent Applications Nos. 105861/74 and 139935/74 (now Pat. Disc. Numbers 32317/76 and 65928/76, respectively) for simplification of the former method. With these methods, one cycle of a required musical waveshape is divided by a straight-line approximation at irregular (Pat. Appln. No. 105861/74) or regular (Pat. Appln. No. 139935/74) time intervals into a plurality of periods and data such as inclination and amplitude variations and time information (Pat. Appln. No. 10586/74) of the waveshape of each period are stored in a memory. This remarkedly reduces the memory capacity used, and enables an increase in the number of quantizing steps with the small memory capacity, providing the advantage of alleviation of quantizing noise.
The tone source devices set forth in the abovesaid Japanese patent applicaions are advantageous for substantially faithful reproduction of a sound of an actual musical instrument. For simultaneous generation of a plurality of sounds which is peculair to the electronic musical instrument, however, it is necessary to provide a plurality of waveshape memories, which inevitably introduces bulkiness in the device.
To avoid the abovesaid defect, the assignee of the present application has further proposed a novel method of Japanese Patent Application No. 79673/75 (now Pat. Disc. No. 3421/77). With this method, one cycle of a required musical waveshape is divided into a plurality of periods and information such as inclination and amplitude variations of the waveshapes of each period is stored in a memory and read out therefrom on a time shared basis, by which waveshapes of different frequencies can be simultaneously obtained based on each waveshape information. In this manner, a plurality of sounds can be simultaneously produced without the necessity of increasing the memory capacity used.
Further, the assignee of the present application has proposed in Japanese Patent Application No. 96035/75 (now Pat. Disc. No. 45322/77) improvements in the key assignor method in which a key depression or release signal sent out in the form of a coded digital signal is selectively applied to tone source circuits.
Moreover, since the frequency spectrum contained in a musical waveshape of an actual instrument sound differs for each sound range, it is difficult to simply approximate the instrument sound with one musical waveshape.